The present invention relates to a wave device for combining power at microwave/radio frequencies.
Solid state devices are low power and, with increasing frequency, the power output from a single solid state device decreases rapidly. In many applications, the power levels that are required exceeded the capability of any single device or amplifier. It is therefore desirable to extend the power level by combining techniques to take advantage of the many desirable features of solid state devices, such as small size and weight, reliability and performance in a broader range of applications. Many types of power combiner are known and these have applications in many areas, such as cellular radio base stations, broadcast services, earth stations, radar and antennas.
A significant problem with known power combiners occurs upon failure of one of the input power amplifiers.
FIG. 1 of the accompanying drawings illustrates a microstrip layout of a 2-way Wilkinson combiner. This combiner performs adequately as long as the power amplifiers on both of its inputs are functioning correctly. However, this combiner requires the impedance at both inputs to be balanced. If the power amplifier at one input fails, then power from the other input is out of balance and performance drops significantly. Indeed, it can become very difficult, if not dangerous, to attempt to replace the failed power amplifier, since disconnection of the failed power amplifier from its input may result in transmission of waves from that input to the service engineer.
For previously known methods of power combinations, the following efficiencies are available for a 2-amplifier arrangement under fully working conditions and with a single amplifier failure:
Wilkinson:
No failure: 90%,
Single amplifier failure 40%;
Directional Coupler:
No failure: 90%,
Single amplifier failure 39%;
N-way hybrid combiner:
Single amplifier failure: 25%;
Planar:
Single amplifier failure: 25%.
Description of the N-way hybrid combiner and the planar device may be found respectively in A. A. M. Saleh, xe2x80x9cImproving the Graceful-Degradation Performance of Combined Power Amplifiersxe2x80x9d IEEE Trans. Microwave Theory Tech, Vol. MTT-28, No. 10, October 1980, pp 1068-1070 and I. J. Bahl and . Bhartia, Microwave Solid State Circuit Design, Wiley, N.Y., 1988.
Hence, it is an object of the present invention to provide a combiner of improved sufficiency, particular upon failure of an input amplifier.
According to the present invention there is provided a method of combining electromagnetic waves comprising:
arranging a first pair of inputs across a wave device so as to set up a first standing wave therebetween;
arranging a second pair of inputs across the wave device so as to set up a second standing wave therebetween such that the input independence of each of the first and second pairs of inputs is unaffected by the other of the first and second pairs of inputs; and
arranging an output at a position on the wave device so as to receive power from both the first and second standing waves.
According to the present invention there is provided a wave device for supporting electromagnetic waves, the device including:
a first pair of inputs for setting up a first standing wave therebetween;
a second pair of inputs for setting up a second standing wave therebetween and positioned such that the input signal of each of the first and second pairs of inputs is unaffected by the state or impedance of the other of the first and second pairs of inputs; and
an output positioned so as to receive power from both the first and second standing waves.
In this way, since the inputs to the wave device are arranged in pairs, any failure results in a symmetric loss of input to the wave device, furthermore, since pairs of inputs are positioned on the device such that they have no effect on the other inputs, any failure will not affect the balance of the other inputs. Failure of one pair of inputs merely results in a corresponding loss of power at the output.
An additional advantage is that, since each pair of inputs receives no power from the other pair of inputs, upon failure of an input amplifier, that input amplifier can be disconnected and replaced without any danger of transmission from the disconnected input.
The wave device may include a conductive plate for supporting the first and second standing waves. The plate may be mounted parallel to a grounded structure and separated from the grounded structure by a dielectric. In this way, the device may be constructed as a microstrip structure. Such structures are well known and may be easily produced by the skilled person.
The plate may be a polygon having an even number of sides with each respective pair of inputs connected across an opposing pair of sides. Alternatively, the plate may be circular, such that each respective pair of inputs is connected to the plate across a diameter of the plate.
In this way, the invention may be carried out with the pairs of inputs angularly displaced around the perimeter of the plate.
Preferably, the output is positioned at substantially the antinode of the device which may be preferably the centre of the device.
In this way, the output may easily receive power from both of the standing waves.
Preferably the device further comprises first and second dividers for providing the first and second pairs of inputs from first and second signal sources. In this way, power from a single signal source is evenly divided between a pair of inputs, such that power is input across the device evenly.
The device may comprise one or more additional pairs of inputs for setting up additional respective standing waves.
In this way, the combiner may combine three or more signals, with each signal being independent of the other signals and not effecting the input impedance.
The wave device may also be used as a splitter by providing a power input at the output of the wave device and receiving divided power output from the pairs of inputs.